Aquaculture system and processes for growing fish, under controlled conditions are well known. These systems and processes may be open (i.e. water is constantly replenished from an outside source) or closed (i.e. water is continuously cleaned, aerated and recirculated through the system).
To date, the vast majority of fresh-water aquaculture involves either the culture of catfish or trout, in open systems, requiring stringent levels of water resource availability and complimentary climatic conditions. Furthermore, operating costs associated with such open systems are substantial in that they usually require relatively large tracts of land and substantial electrical and mechanical energy for maintaining water quality levels.
A closed-loop aquaculture system offers many advantages over an open system. For example, since water is constantly reused, expenses for supplying, moving and storing water is minimized. Additionally, the expenses associated with maintaining water temperature in a closed-loop system are considerably lessened, since once a volume of water is brought to a desired temperature, little energy is required to maintain that temperature. Also, undesirable fluctuations in temperature and water quality can be eliminated.
Closed-loop aquaculture systems are disclosed, for example, in "Home Aquaculture: A Guide to Backyard Fish Farming" by S. D. VanGorder (inventor herein) and D. J. Strange, Rodale Press, 1983. That publication, which is incorporated herein by reference, discloses season-dependent, single tank, small-scale aquaculture systems. These sytems are usually comprised of a twelve by three foot swimming pool, which serves as the fish culture tank. According to the methods disclosed in that reference, fish are raised from fingerling size to about one pound during the course of a growing cycle, which takes place in a single tank. The growing cycle, from stocking of the fingerlings to harvest of the mature fish is normally about six months.
Another aquaculture system is disclosed in U.S. Pat. No. 4,030,450, which pertains to a method and apparatus for aquaculture in a recirculating closed-loop system. In general, the method and apparatus of that patent provide for continuously maintaining and feeding food to fish for a period of months until they reach marketable size. The preferred water to fish ratio is at least about one fish per gallon of water. Water recirculation is intermittent and is dependent on fish size, since circulation is less necessary when the cultured fish are small than when they are more fully grown.
Other aquaculture systems and methods include those disclosed in U.S. Pat. No. 3,973,519 pertaining to a screening apparatus for retaining small marine animals in a growing container connected to a closed-loop aquaculture system; U.S. Pat. No. 3,761,262 pertaining to a filtration and circulation system for maintaining water quality in a fish tank; U.S. Pat. No. 3,661,119 pertaining to a fish larvae rearing tank and an associated circulation and filtration system associated therewith; and U.S. Pat. No. 4,212,268 pertaining to an aquaculture habitat for the rearing of post-larval crustacea in a cellular honeycomb structure.
In a typical fish aquaculture system, fish are stocked at whatever density is necessary to reach the capacity of the system when the fish have reached harvest size. For example, if an acre catfish pond is expected to produce 5,000 pounds of one pound fish, then 5,000 fingerling fish are stocked in the spring, and fed at that density throughout the summer. Of course, this means that for most of the entire growing season, the pond is being used to much less than its capacity of 5,000 pound of fish.